Rewrote readme

README.md

@@ -2,37 +2,138 @@
 
 
 ## Overview
-This part of the backend handles device push notifications for registered users. It consumes messages from RabbitMQ, looks up user device tokens from a MySQL database, and sends notifications via Expo's API. Failed deliveries are retried or sent to a dead-letter queue.
+
+This service consumes messages from RabbitMQ, retrieves encrypted push tokens from a MySQL database, decrypts them, and sends notifications via the Expo Push API. It includes comprehensive error handling, automatic retries, dead-letter queuing, and Prometheus metrics.
 
 
-## Requirements
-- Python 3.12+
-- MySQL database
-- RabbitMQ
-- Python packages from requirements.txt
+## Features
+
+- **Asynchronous Architecture**: Built with `asyncio`, `aio_pika`, and `aiomysql` for high-performance concurrent operations
+- **Automatic Retry Logic**: Failed notifications are automatically retried up to 5 times with exponential backoff
+- **Dead Letter Queue (DLQ)**: Messages that exceed retry limits are moved to a DLQ for manual inspection
+- **Health Monitoring**: Database connection pool health checks every 60 seconds
+- **Prometheus Metrics**: Real-time monitoring of queue depths and message processing stats
+- **Token Management**: Automatically expires invalid or unregistered device tokens
+
+## Architecture
+
+```
+RabbitMQ → Consumer → Database Lookup → Token Decryption → Expo Push API
+                ↓                                              ↓
+           Retry Queue ←─────────── Delivery Validation ──────┘
+                ↓
+           Dead Letter Queue
+```
+
+## Prerequisites
+
+- Python 3.10+
+- MySQL/MariaDB database
+- RabbitMQ server
+- Expo Push Notification service account
+
+## Installation
+
+```bash
+pip install -r requirements.txt
+```
+
+## Running the Service
+
+```bash
+python rabbitmq_handler.py
+```
+
+The service will:
+1. Connect to the MySQL database
+2. Establish RabbitMQ connection and declare queues
+3. Start consuming messages
+4. Begin Prometheus metrics server on port 9000
 
 
 ## Configuration
 
-**Environment variables:**
+### Database Manager (`db.py`)
 
-- `LOG_LEVEL` (DEBUG, INFO, WARNING, ERROR, CRITICAL)
+- **Pool Size**: 5 connections (configurable)
+- **Health Check Interval**: 60 seconds
+- **Auto-commit**: Enabled
+- **Cursor Type**: DictCursor for convenient row access
 
-- `RABBITMQ_URL`
+### RabbitMQ Consumer (`rabbitmq_handler.py`)
 
-- `MYSQL_HOST`, `MYSQL_USER`, `MYSQL_PASSWORD`, `MYSQL_DATABASE`
+- **Queue Name**: `notifications`
+- **Retry Queue**: `notifications_retry`
+- **Dead Letter Queue**: `notifications_dlq`
+- **Max Retries**: 5 attempts
+- **Retry TTL**: 30 seconds
+- **Routing Key**: `notify.user.*` (standard), `notify.user.retry` (retries)
 
-- `API_ENDPOINT` (Expo push API)
+### Notification Sender (`send_notification.py`)
 
+- **Endpoint**: `https://exp.host/--/api/v2/push/send`
+- **Max Retries**: 5 attempts
+- **Timeout**: 5 seconds per request
+- **Backoff Strategy**: Exponential (2^attempt seconds)
 
-## Metrics
+### Message Format
 
-Metrics are exposed on port `9000` for Prometheus, including:
+Messages should be published to RabbitMQ with the following structure:
 
-- `MSG_PUBLISHED`
+```json
+{
+	"title": "New Message",
+	"body": "You have a new notification",
+	"data": {
+		"category": "utility",
+		"link": "https://example.com",
+		"timestamp": "1760734800"
+}
+```
 
-- `MSG_FAILED`
+**Routing Key**: `notify.user.<user_id>` or `notify.user.retry` for retries
 
-- `MSG_RETRY`
+### Retry Messages
 
-- Queue sizes
+Retry messages include additional metadata:
+
+```json
+{
+  "title": "Notification Title",
+  "body": "Notification message body",
+  "uuid": "device-uuid-here",
+  "retry_count": 2
+}
+```
+
+## Delivery Validation
+
+The service validates delivery results from the Expo Push API:
+
+| Status | API Status | Action |
+|--------|-----------|--------|
+| `ok` | `ok` | Success - metric incremented |
+| `ok` | `error` (DeviceNotRegistered) | Token expired in database |
+| `ok` | `error` (other) | Sent to DLQ |
+| `error` | - | Sent to DLQ |
+| `failure` | - | Requeued for retry |
+
+## Monitoring
+
+### Prometheus Metrics
+
+Available at `http://localhost:9000/metrics`:
+
+- `msg_published_total`: Successfully delivered notifications
+- `msg_retry_total{queue_name, uuid, retry_count}`: Retry attempts
+- `msg_failed_total`: Failed deliveries
+- `queue_depth{queue_name}`: Current queue message counts
+
+## Troubleshooting
+
+### Connection Issues
+- `aiomysql` uses `PyMySQL` which requires the `mysql_native_password` plugin to be used. Can be checked and changed via:
+```sql
+SELECT user, host, plugin FROM mysql.user WHERE user='backend-push-notifications';
+ALTER USER 'backend-push-notifications'@'%' IDENTIFIED WITH mysql_native_password BY 'db_password';
+```